I have some Oregon Scientific units for the house and they work well. But, we have used cheapo ones for the trailer and they don't work well. Batteries don't last and since we just put the sensor in the bumper, the sun always shines on it (even if it faces north), it isn't accurate during the day when it works. There's enough metal between the dinette and bumper to probably affect the reception from the sensor, but any outside mounting I can think of doesn't do the sensor any good either. When it working well, I can get the temps inside the trailer (sensor there) on the monitor in the house from 100+ feet away. This is helpful before I winterize it and am still taking trips. Then I know when to turn on the furnace and set it at 40˚
Opening the door and sticking my head out works better, but my head doesn't always work well either.
I also get local weather forecasts on my laptop when I can and that'll tell me what to expect (most of the time).
The main reason I want one is to see how cold it is getting at night to know whether to turn the furnace on to keep the fresh water tank from freezing (especially when it is parked at home). Since I always wake up in the middle of the night, I check the temp then and if the temp is getting below 40˚ outside, I turn on the furnace. The catalytic heater doesn't keep the trailer warm enough at those temps and the heat pump is noisy and fairly ineffective below 40˚. If we are boondocking, I set the furnace for 50˚. Then Barb sets it for the upper 50's, and then I turn it down. She turns it back up. I give up.